Synthesis and linear optical properties of tris(catecholato)metal(III,IV) complexes with acceptor-substituted ligands

Article abstract of DOI:10.1002/ejic.200500401

The synthesis of C₃-symmetric chromophores (2-4, 9, 10, 14) with acceptor-substituted catecholato ligands and different central metal atoms (Si, Al, Ti) is described. These complexes might serve as octupolar chromophores with first-order nonlin

Full text of DOI:10.1002/ejic.200500401

FULL PAPER
Synthesis and Linear Optical Properties of Tris(catecholato)metal(III
Complexes with Acceptor-Substituted Ligands
,IV)
Volker Kriegisch[a] and Christoph Lambert*[a]
Dedicated to the memory of Prof. Dr. Rüdiger Wortmann (1959–2005)
Keywords: Nonlinear optics / Octupolar complexes / Chromophores / Donors / Acceptors / Catecholate
The synthesis of C3-symmetric chromophores (2–4, 9, 10, 14)
with acceptor-substituted catecholato ligands and different
central metal atoms (Si, Al, Ti) is described. These complexes
might serve as octupolar chromophores with first-order non-
linear optical properties. UV/Vis spectroscopic investigations
show a red-shift of the lowest-energy charge-transfer band
on going from SiIV, AlIII to TiIV complexes, dependent on the
increasing ionic character of the M–O bond.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
While most NLO chromophores are one-dimensional
and show, owing to the difference of the ground- and ex-
cited-state dipole moments, a strong solvatochromism,
there are also D3-symmetrical two-dimensional “octupolar”
NLO chromophores which have the advantage that they do
not show solvatochromism and, therefore, no loss of trans-
parency in a polar environment. This is a consequence of
the vanishing dipole moments in a D3-symmetric chromo-
phore.[9–11] Therefore, in recent years many investigations
were devoted to this type of NLO chromophore.[2,12–16]
Although Brooker’s dye shows exceptionally high qua-
dratic NLO properties, its accurate investigation is ham-
pered because of the sensitivity of the electronic structure
to protonation or even because of hydrogen bonding of the
phenolate oxygen atom.[17–23] Therefore, the goal of this in-
vestigation is to synthesise octupolar chromophores in
which the phenolate part of a chromophore ligand is com-
plexed by a metal ion in order to reduce its sensitivity to
protic impurities. On the other hand, the metal ion serves
as a template to organise three chromophores in a threefold
symmetric arrangement. In order to gain thermodynamic
stability, we used ligands based on catecholate rather than
on phenolate as in Brooker’s dye. The metal ions are
Introduction
Over the past two decades, there has been considerable
interest in the nonlinear optical (NLO) properties of organic
and organometallic materials because of their potential ap-
plication in various fields such as telecommunications, op-
tical data storage and optical information processing. Many
organic chromophores possess very high NLO efficiencies
which derive from the high polarisability of electrons in un-
saturated systems.[1–6] In one-dimensional NLO chromo-
phores, in which a π-system is terminated by an electron
acceptor and a donor, the electronic structure can be de-
scribed by a mixture of a neutral valence-bond structure and
a polar charge-separated mesomeric structure. The dipole
moments of the ground and the first excited charge-transfer
(CT) state depend on the degree of mixing. Those species,
in which the neutral mesomeric structure constitutes the
major part of the ground-state wave function, have a small
ground-state dipole moment but a high dipole moment in
the excited state. The prototype is 4-(dimethylamino)-4Ј-ni-
trostilbene (DANS).[3,4] Those systems, in which the dipolar
mesomeric structure is the one which dominates the ground
state, display zwitterionic character in the ground state but
have a small dipole moment in the excited state. Brooker’s
dye is the prototype.[7,8]
AlIII [24] TiIV,[25–27] and SiIV[28,29] because these ions are
,
known to form stable complexes with catecholate. The ions
also form highly polar bonds to oxygen atoms, which will
allow the catecholate to retain most of its anionic electronic
structure, which is important in order to serve as a good
electron donor in the ligand chromophores. The ligands
used are given below. While 1 is derived from caffeic acid
that has a carboxylic ester function as the electron acceptor,
the ligands 8 and 13 have a nitro and a trimethylammonio
group, respectively, as the acceptor functionalities. In the
[a] Universität Würzburg, Institut für Organische Chemie,
Am Hubland 1, 97074 Würzburg, Germany
Fax: +49-931-888-4606
E-mail: lambert@chemie.uni-wuerzburg.de
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DOI: 10.1002/ejic.200500401
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forthcoming sections we describe the syntheses and the lin- TiIV complex 2 has been prepared in high yield using a pro-
ear optical properties of some metal complexes derived cedure by Albrecht et al.[25,30]
from the above-mentioned ligands.
To explore the preparation of tris(catecholato) complexes
with different central atoms, 1 was used as an easily access-
ible ligand. In case of the TiIV and AlIII complexes Li2CO3
was used as the base. For the SiIV complex 3 triethylamine
was used as the base for the preparation. NMR and IR
spectroscopic investigations confirm the formation of the
complexes. An intense band occurs in the IR spectra at
about 1200–1300 cm–1 which is typical of C–O stretching
modes in catecholato–metal structures.[24,31] In the case of
the unsymmetrical ligand 1 diastereomeric complexes form
which we were unable to separate. These diastereomers are
likely to show slightly different optical properties, which are
not considered in the following text.
Results and Discussion
In order to avoid problems with diastomeric mixtures, 4,5-
substituted catecholate systems were used to synthesise D3-
symmetrical complexes that will only consist of enantiomers.
The ligands 8 and 13 were prepared starting from the
tert-butyldimethylsilyl-(TBDMS-)protected diiodo com-
pound 5 which was synthesised according to Lulinski et al.
and Kinder et al.[31,32] Using Hagihara coupling reaction
conditions, compound 5 and 2 equiv. of 6 gave the 4,5-di-
substituted ligand 7 in 75% yield. The reaction time has to
be limited to 2 h because of the increasing formation of by-
products with a prolonged reaction time. Deprotection of
the TBDMS group led to the catechol ligand 8 in high
yields (Scheme 2). The TiIV (9) and SiIV complexes (10)
were prepared in the same way as the caffeic acid com-
plexes. Although the corresponding AlIII complex could be
synthesised in an analogous manner, we were unable to pu-
Synthesis and Characterisation
The synthesis of the (catecholato)M (M = metal) com-
plexes 2–4 is illustrated in Scheme 1. The tris(catecholato)-
Scheme 1. Synthesis of octupolar (catecholato)MIV,III complexes 2–4. rify this complex.
Scheme 2. Syntheses of the acceptor-substituted catechol ligand 8 and the corresponding octupolar TiIV (9) and SiIV complexes (10).
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Tris(catecholato)metal(,) Complexes with Acceptor-Substituted Ligands
FULL PAPER
Scheme 3. Syntheses of the TBDMS-protected acceptor-substituted catechol ligand 13 and the corresponding octupolar TiIV complex 14.
Ligand 13 was built up in the same way as alkyne 8:
The reason for this behaviour is, as for ligand 8, the con-
the alkyne 11 was coupled with 5 in a palladium-catalysed centration-dependent shift of the acid/base equilibrium to
reaction to give compound 12. Subsequently, the amino the deprotonated species and finally to the catecholate di-
groups of 12 were quaternised with methyl iodide. The TiIV anion 12–. Quantitative preparation of the catecholate di-
complex 14 was prepared by in situ deprotection of 13 and anion 12– by adding sodium tert-butoxide to a solution of
reaction with TiO(acac)2 (Scheme 3).
1 results in a bathochromic shift and in the formation of an
intense band at λmax = 420 nm which corresponds to the
one observed for 1 at high dilution. In contrast to 1 the
UV/Vis spectra of the metal complexes 2–4 in DMSO,
DMF and MeCN are concentration-independent. Com-
parison of the UV/Vis spectra of the tris(catecholato)M
complexes of 1 in DMSO with that of 12– shows a hypso-
chromic shift of the absorption maximum for M = SiIV (3)
(λmax = 394 nm) over AlIII (4) (λmax = 404 nm) to TiIV (2)
(λmax = 423 nm). The latter shows a maximum at about
the same wavelength as the free ligand 12– (Figure 2). This
behaviour reflects the different degree of ionicity in the M–
O bond increasing from SiIV–O over AlIII–O to TiIV–O. The
high ionicity of the M–O bond concentrates charge on the
catecholate oxygen atoms, which become stronger donors
the more ionic the bond is. This results in an intraligand
CT absorption as observed in, for example, other tris(cate-
cholato)TiIV complexes.[26] Interestingly, the band width of
this CT band is much broader for 2 than for 3 and 4.
Whether this effect has to do with diastereomeric mixtures
or is due to electronic effects is presently unclear.
UV/Vis Absorption Spectra
Owing to the ionic character of all complexes, absorption
spectra could only be recorded in relatively polar solvents.
The UV/Vis spectra of the free ligand 1 show a concentra-
tion-dependent behaviour in DMSO. At high concentra-
tions 1 has an absorption maximum at λmax = 335 nm. Di-
lution leads to the formation of a new band at 425 nm,
associated with an increase of this band (Figure 1).
While the spectra of 2–4 do not vary much in DMSO,
DMF and MeCN, further studies of their possible solva-
tochromism were hampered by the insolubility in less polar
solvents. In MeOH decomposition of 3 was observed and
free ligand 1 was formed.
The complexes 9 and 10 show a similar behaviour of the
absorption spectra as the complexes 2–4 (Figure 3). The
spectra of both compounds 9 and 10 are shifted batho-
Figure 1. Concentration-dependent UV/Vis spectra of 1 and the
catecholate 12– in DMSO.
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Table 1. UV/Vis data {λmax [nm] (ε [–1cm–1])} of ligands 1, 8, 13,
the corresponding catecholates 12–, 82– and tris(catecholato)MIII,IV
complexes 2–4, 9, 10, 14.
DMSO
DMF
MeCN
1
12–
2
340 (17100)
420 (34261)
423 (43300)
394 (65200)
404 (56100)
377 (20500)
531 (14813)
460 (68100)
442 (60900)
292 (21400)
391 (63600)
426 (46400)
394 (69800)
408 (61800)
409 (41000)
378 (67000)
3
4
8
82–
9
463 (70900)
447 (62200)
446 (71200)
429 (69100)
10
13
14
397 (64800)
389 (65500)
Figure 2. Absorption spectra of tris(catecholato)M complexes 2–4
and of catecholate 12– in DMSO.
chromically vs. the free ligand 8. Even here the increasing
ionic character of the MIV–O bonding is responsible for the
red shift of the absorption maximum of the SiIV compound
10 vs. the TiIV compound 9. In DMSO the band maximum
for 9 is at λmax = 460 nm and for 10 at λmax = 442 nm.
Surprisingly, even the absorption maximum of the TiIV
complex 9 does not reach that of the free deprotonated li-
gand 82–. This contrasts the behaviour of 2. Neither the free
ligand 8 nor the complexes themselves show fluorescence in
DMSO, but their absorption is slightly solvatochromic (see
Table 1). Ligand 8 shows, as for ligand 1, a concentration-
dependent deprotonation of the hydroxy groups to form the
catecholate 82–. Although the TiIV complex 9 has a higher
stability compared to the SiIV species 10, we observe ligand
exchange in methanol.
Figure 4. Absorption spectra of tris(catecholato)M complex 14 and
ligand 13 in DMSO.
Conclusions
Although we could not measure the absorption spectra
of the metal catecholates in solvents with strongly different
polarity due to solubility/instability problems, the bathoch-
romic shift of the lowest-energy transition for the ligands 1
and 8 on going from SiIV via AlIII to TiIV complexes 2–4,
9, and 10 supports the assignment to an intraligand charge-
transfer transition. The bathochromic shift of this transi-
tion reflects the increasing ionic character of the M–O
bonding which in turn causes the catecholate oxygen atom
to become a stronger donor in the TiIV complexes than in
the SiIV compounds. For this reason the spectroscopic prop-
erties of the TiIV complexes 2 and 9 approach those of the
deprotonated free ligands 12– and 82–. The higher energy
transition of TiIV complex 14 compared to 9 reflects the
much weaker electron acceptor strength of the trimethylam-
monio substituent compared to the nitro group.[33] The for-
mer substituent acts by a purely inductive (field) effect while
in the latter mesomeric effects also play a role.
Figure 3. Absorption spectra of the tris(catecholato)M complexes
9, 10 and the corresponding ligand 8 and catecholate 82– in DMSO.
In conclusion, we were able to synthesise a series of octu-
The UV/Vis spectrum of 14 in DMSO is similar to the polar chromophores and to characterise their linear optical
spectrum of 9 but has a maximum at λmax = 391 nm which properties. The metal complexes described in this paper can
is blue-shifted vs. 9 due to the R3N+ electron acceptor that serve as reasonably stable substitutes for the much more
is weaker than the NO2 group in 9 (Figure 4).
sensitive free-ligand chromophores. Owing to their intense
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Tris(catecholato)metal(,) Complexes with Acceptor-Substituted Ligands
FULL PAPER
(m), 1354 (w), 1259 (s, C–O), 1157 (s), 1117 (m), 1035 (vw), 985
intraligand CT transitions these complexes might be good
candidates as chromophores for first-order nonlinear appli-
cations.[34]
(vw), 926 (vw), 835 (m), 790 (w), 694 (m), 578 (vw), 523 (w) cm–1.
Trilithium Tris{4-[2-(methoxycarbonyl)ethenyl]-1,2-benzenediolato}-
aluminate(III) (4): To a mixture of methyl 3-(3,4-dihydroxy)phenyl-
2-propenoate (1; 300 mg, 1.54 mmol) and Li2CO3 (56.2 mg,
758 µmol) in dry MeOH (15 mL) Al(acac)3 (165 mg, 509 µmol) was
added. The solution turned yellow and was stirred at room tem-
perature for 24 h. The solvent was removed in vacuo, the remaining
yellow solid was suspended in hot ethyl acetate and filtered off. The
precipitate was washed twice with hot ethyl acetate and dried in
Experimental Section
General Remarks: All operations were performed under nitrogen or
argon using standard Schlenk-line techniques. All reagents were
purchased from commercial sources and used as received. Methyl
3-(3,4-dihydroxy)phenyl-2-propenoate (1),[35] 1,2-bis(tert-butyldi-
methylsilyloxy)-4,5-diiodobenzene (5),[31] 1-ethynyl-4-nitrobenzene
(6),[36] and (4-ethynylphenyl)dimethylamine (11)[36] were prepared
according to literature procedures.
1
vacuo. Yield 84% (268 mg) of a yellow solid. H NMR (250 MHz,
3
[D4]methanol, 25 °C): δ = 7.49 (d, JHH = 15.4 Hz, 1 H, CH=CH),
4
3
4
6.78 (d, JHH = 1.8 Hz, 1 H, 3-H), 6.57 (dd, JHH = 7.9, JHH
=
1.8 Hz, 1 H, 5-H), 6.42 (d, 3JHH = 7.9 Hz, 1 H, 6-H), 6.00 (d, 3JHH
= 15.5 Hz, 1 H, CH=CH), 3.70 (s, 3 H, MeO) ppm. 13C NMR
(62.9 MHz, [D4]methanol, 295 K): δ = 171.3, 162.0, 156.4, 150.3,
123.3, 123.0, 112.9, 110.0, 108.5, 51.6 ppm. C30H24AlLi3O12·5H2O
(714.34): calcd. C 50.44, H 4.80; found C 50.79, H 4.84. IR (KBr):
Instrumental: 1H and 13C NMR spectra were recorded with a
Bruker Avance 400 FT NMR spectrometer. Elemental analyses
were obtained from the Institut für Anorganische Chemie of the
Universität Würzburg using an apparatus from Leco (CHNS-932).
Infrared spectra were recorded in the range 4000–200 cm–1 as KBr
pellets with a Jasco 410 FT-IR spectrometer. UV/Vis spectra were
recorded with a Jasco V-570 UV/Vis/NIR spectrometer using Uva-
sol® solvents from Merck.
ν = 3054 (vw, aryl-C–H), 2984 (w, C–H), 1685 (m, C=O), 1622 (m),
˜
1582 (m), 1497 (s), 1437 (m), 1346 (vw), 1269 (s, C–O), 1199 (m),
1166 (m), 1120 (w), 1042 (vw), 980 (w), 929 (vw), 827 (w), 784 (vw),
655 (w), 616 (w) cm–1.
1,2-Bis(tert-butyldimethylsilyloxy)-4,5-bis[2-(4-nitrophenyl)ethynyl]-
benzene (7): To a mixture of 4,5-bis(tert-butyldimethylsilyloxy)-1,2-
diiodobenzene (5; 189 mg, 320 µmol), (PPh3)2PdCl2 (24.0 mg,
34.2 µmol) and CuII (4.00 mg, 21.0 µmol) in dry Et2NH (5 mL)
was added 1-ethynyl-4-nitrobenzene (6; 100 mg, 680 µmol). The red
solution was heated to 60 °C for 1 h, cooled to room temperature
and the solvent was evaporated in vacuo. The remaining black solid
was purified by flash chromatography on silica gel (dichlorometh-
ane/petroleum ether, 2:3) to yield a yellow solid. The solid was dis-
solved in dichloromethane and the solution added dropwise to pe-
troleum ether. The dichloromethane was removed in a rotary evap-
orator, the precipitate was filtered and dried in vacuo. Yield 75%
Dilithium Tris{4-[2-(methoxycarbonyl)ethenyl]-1,2-benzenediolato}-
titanate(IV) (2): To a mixture of methyl 3-(3,4-dihydroxy)phenyl-2-
propenoate (1; 250 mg, 1.28 mmol) and Li2CO3 (32.0 mg,
433 µmol) in dry MeOH (15 mL) TiO(acac)2 (112 mg, 430 mmol)
was added. The solution turned deep red and was stirred at room
temperature for 24 h. The solvent was removed in vacuo, the red
solid was dissolved in ethyl acetate and carefully covered with a
layer of petroleum ether. The crystalline precipitate was filtered off,
washed with petroleum ether and dried in vacuo to yield a red
solid. Yield 72% (225 mg). 1H NMR (250 MHz, [D6]acetone,
25 °C): δ = 7.49 (d, 3JHH = 15.9 Hz, 1 H, CH=CH), 6.72 (dd, 3JHH
4
4
= 8.2, JHH = 2.2 Hz, 1 H, 5-H), 6.56 (d, JHH = 2.1 Hz, 1 H, 3-
1
3
3
(163 mg) of a yellow solid. H NMR (250 MHz, CDCl3, 25 °C): δ
H), 6.23 (d, JHH = 7.9 Hz, 1 H, 6-H), 6.06 (d, JHH = 15.9 Hz, 1
H, CH=CH), 3.67 (s, 3 H, MeO) ppm. 13C NMR (62.9 MHz, [D6]-
acetone, 295 K): δ = 168.3, 160.6, 147.9, 125.0, 122.7, 112.2, 111.6,
109.9, 106.1, 51.2 ppm. C30H24Li2O12Ti·5H2O (728.35): calcd. C
= 8.22 (AAЈ, 4 H), 7.65 (BBЈ, 4 H), 7.03 (s, 2 H, 3-H, 6-H), 1.01
[s, 18 H, (CH3)3CSi], 0.26 [s, 12 H, (CH3)2Si] ppm. 13C NMR
(62.9 MHz, CDCl3, 295 K): δ = 149.5, 148.2, 133.2, 130.7, 125.3,
124.8, 119.6, 93.3, 91.7, 26.2, 19.2, –3.85 ppm. C34H40N2O6Si2
(677.24): calcd. C 64.94, H 6.41, N 4.45; found C 64.69, H 6.24, N
49.47, H 4.71; found C 49.69, H 5.13. IR (KBr): ν = 3052 (aryl-C–
˜
H), 3016 (w, aryl-C–H), 2975 (w, C–H), 1686 (m, C=O), 1624 (m),
1579 (w), 1486 (s), 1436 (m), 1261 (s, C–O), 1197 (w), 1118 (w),
1042 (vw), 977 (vw), 824 (w), 641 (m), 613 (w), 505 (w) cm–1.
4.52. IR (KBr): ν = 3041 (vw, aryl-C–H), 2951 (w, C–H), 2930 (w,
˜
C–H), 2857 (w, C–H), 2204 (vw, CϵC), 1592 (m), 1536 (w), 1510
(s, NO2), 1410 (w), 1345 (w), 1336 (s, NO2), 1256 (m), 1213 (vw),
1105 (w), 1083 (w), 939 (m), 886 (vw), 871 (w), 848 (m), 843 (m),
783 (w), 748 (vw), 684 (vw) cm–1.
Bis(triethylammonium)
Tris{4-[2-(methoxycarbonyl)ethenyl]-1,2-
benzenediolato}silicate(IV) (3): To a mixture of methyl 3-(3,4-dihy-
droxy)phenyl-2-propenoate (1; 250 mg, 1.28 mmol) and Et3N
(119 mg, 908 µmol) in dry MeOH (5 mL) Si(MeO)4 (63.9 mg,
409 µmol) was added. The solution turned yellow and was stirred
at room temperature for 24 h. The solvent was removed in vacuo.
The yellow solid was dissolved in dichloromethane and the solution
added dropwise to petroleum ether. The precipitate was filtered off,
washed with petroleum ether and dried in vacuo. Yield 88%
1,2-Dihydroxy-4,5-bis[2-(4-nitrophenyl)ethynyl]benzene (8): To a
solution of 1,2-bis(tert-butyldimethylsilyloxy)-4,5-bis[2-(4-ni-
trophenyl)ethynyl]benzene (7; 95.0 mg, 140 µmol) in dry THF
(10 mL) tetrabutylammonium fluoride (101 mg, 386 µmol, 1 
solution in THF) was added. The deep purple solution was stirred
at room temperature for 30 min and a cold H3PO4 solution (30 mL,
1 ) was added. The mixture was extracted with Et2O (3×30 mL).
(300 mg) of a yellow solid. 1H NMR (250 MHz, [D4]methanol,
3
25 °C): δ = 7.53 (d, JHH = 15.5 Hz, 1 H, CH=CH), 6.86 (s, 1 H, The organic phases were combined, dried with Na2SO4 and the
3-H), 6.72 (d, 3JHH = 7.9 Hz, 1 H, 6-H), 6.53 (dd, 3JHH = 8.0, 4JHH
solvent was removed in vacuo. The remaining brown solid was
purified by flash chromatography on silica gel (ethyl acetate/n-hex-
3
= 1.2 Hz, 1 H, 5-H), 6.13 (d, JHH = 15.5 Hz, 1 H, CH=CH), 3.72
(s, 3 H, MeO), 3.08 (q, 12 H, CH3CH2N), 1.21 (t, 18 H, CH3CH2N) ane/CH3COOH, 10:25:1) to yield an orange solid. The solid was
ppm. 13C NMR (62.9 MHz, [D4]methanol, 295 K): δ = 170.9,
dissolved in ethyl acetate and the solution added dropwise to n-
156.5, 152.6, 149.5, 125.5, 123.6, 111.8, 111.2, 109.2, 50.8, 48.0
hexane. The precipitate was filtered off and dried in vacuo. Yield
(CH3CH2N), 9.62 (CH3CH2N) ppm. C42H58N3O12Si (811.00): 98% (55.0 mg) of an orange solid. 1H NMR (250 MHz, [D6]ace-
calcd. C 62.20, H 7.21, N: 3.45; found C 61.32, H 7.15, N 3.46. IR
tone, 25 °C): δ = 8.31 (AAЈ, 4 H), 7.84 (BBЈ, 4 H), 7.44 (br., 2 H,
HO), 7.17 (s, 2 H, 3-H, 6-H) ppm. 13C NMR (62.9 MHz, [D6]ace-
tone, 295 K): δ = 148.0, 147.9, 133.1, 131.0, 124.8, 119.7, 118.0,
(KBr): ν = 3057 (aryl-C–H), 3019 (w, aryl-C–H), 2986 (w, C–H),
˜
2949 (w, C–H), 1697 (m, C=O), 1623 (m), 1590 (m), 1497 (s), 1447
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94.2, 90.8 ppm. C22H12N2O6·H2O (418.35): calcd. C 63.16, H 3.37,
1,2-Bis(tert-butyldimethylsilyloxy)-4,5-bis{2-[4-(trimethylammonio)-
phenyl]ethynyl}benzene Diiodide (13): To a solution of 1,2-bis(tert-
N 6.70; found C 63.51, H 3.49, N 6.41. IR (KBr): ν = 3480 (br.,
˜
O–H), 3046 (vw, aryl-C–H), 2204 (m, CϵC), 1590 (s), 1508 (s, butyldimethylsilyloxy)-4,5-bis{2-[4-(dimethylamino)phenyl]-
NO2), 1441 (vw), 1349 (s, NO2), 1308 (m), 1261 (w), 1182 (w), 1145
ethynyl}benzene (12; 1.45 g, 2.31 mmol) in THF (20 mL) methyl
iodide (5 mL) was added. The reaction mixture was sealed in a
Schlenk tube and heated to 55 °C for 4 d. Excess methyl iodide
and the solvent were removed in vacuo. The light yellow solid was
dissolved in acetone by heating the mixture to 40 °C, n-hexane was
added and the acetone was removed in a rotary evaporator. The
precipitate was filtered off and washed twice with n-hexane to yield
(w), 1074 (vw), 848 (m), 749 (w), 686 (vw) cm–1.
Dilithium Tris{4,5-bis[2-(4-nitrophenyl)ethynyl]-1,2-benzenediolato}-
titanate(IV) (9): To a mixture of 1,2-dihydroxy-4,5-bis[2-(4-nitro-
phenyl)ethynyl]benzene (8; 50.0 mg, 125 µmol) and Li2CO3
(3.10 mg, 41.9 µmol) in dry MeOH (10 mL) TiO(acac)2 (10.9 mg,
41.5 µmol) was added. The solution turned deep red and was
stirred at room temperature for 24 h. The solvent was removed in
vacuo, the red solid was dissolved in THF and Et2O and carefully
covered with a layer of petroleum ether. Overnight a red solid crys-
tallised which was filtered off and recrystallised from MeCN. Yield
1
a colourless solid. Yield 86% (1.78 g). H NMR (250 MHz, [D6]-
DMSO, 25 °C): δ = 8.06–8.03 (4 H), 7.79–7.74 (4 H), 7.11–7.00 (2
H, 3-H, 6-H), 3.64 (18 H, Me3N), 0.98–0.83 [18 H, (CH3)3CSi],
0.25 to –0.04 [12 H, (CH3)2Si] ppm. 13C NMR (62.9 MHz, [D6]-
DMSO, 25 °C): δ = 147.78, 146.78, 132.51, 132.42, 132.34, 132.24,
124.10, 123.91, 121.29, 121.24, 118.10, 90.26, 89.60, 56.41, 56.34,
25.50, 25.32, 25.26, 18.15, 18.13, 17.72, –3.24, –4.26, –4.54 ppm.
C40H58I2N2O2Si2 (908.89): calcd. C 52.86, H 6.43, N 3.08; found
1
88% (49.0 mg) of a red solid. H NMR (250 MHz, [D4]methanol,
25 °C): δ = 8.25 (AAЈ, 12 H), 7.68 (BBЈ, 12 H), 6.62 (s, 6 H, 3-H,
6-H) ppm. 13C NMR (62.9 MHz, [D4]methanol, 295 K): δ = 161.6,
147.6, 132.5, 132.2, 124.5, 116.4, 115.4, 96.7, 89.9 ppm.
C66H36Li2N6O18Ti·4H2O (1328.86): calcd. C 59.66, H 2.88, N 6.32;
C 52.59, H 6.18, N 3.11. IR (KBr): ν = 3013 (vw, C–H-aryl), 2955
˜
(w, C–H), 2929 (w, C–H), 2885 (vw, C–H), 2857 (w, N–Me), 2210
(vw, CϵC), 1532 (m), 1513 (s), 1492 (m), 1471 (w), 1407 (w), 1357
(m), 1254 (s), 1117 (vw), 1082 (vw), 1013 (vw), 934 (s), 887 (w),
840 (s), 804 (w), 783 (m), 687 (vw), 564 (vw) cm–1.
found C 59.41, H 2.58, N 6.16. IR (KBr): ν = 3056 (vw, aryl-
˜
C–H), 2196 (m, CϵC), 1592 (m, NO2), 1509 (m), 1498 (m), 1477
(m), 1341 (s, NO2), 1241 (s, C–O), 1106 (w), 887 (w), 850 (w), 792
(w), 748 (w), 705 (vw), 687 (vw), 613 (w) cm–1.
Tris(4,5-bis{2-[4-(trimethylammonio)phenyl]ethynyl}-1,2-benzenedi-
olato)titanium(IV) Tetraiodide (14): To a solution of 1,2-bis(tert-bu-
tyldimethylsilyloxy)-4,5-bis{2-[4-(trimethylammonio)phenyl]-
ethynyl}benzene diiodide (13; 200 mg, 220 µmol) in dry MeOH
(13 mL) was added nBu4NF (151 mg, 578 µmol, 1  solution in
THF) followed by TiO(acac)2 (19.2 mg, 73.2 µmol). The solution
turned red and was stirred at room temperature for 24 h. The
orange precipitate was filtered off and washed carefully with
MeOH. The solid was suspended in MeOH (15 mL) and the sus-
pension added dropwise to a concd. solution of NH4(PF6) in
MeOH (10 mL). The precipitate was filtered off and the procedure
was repeated twice to yield an orange solid. Yield 86% (114 mg).
1H NMR (250 MHz, [D6]DMSO, 25 °C): δ = 7.98 (AAЈ, 12 H),
7.70 (BBЈ, 12 H), 6.30 (s, 6 H, 3-H, 6-H), 3.62 (s, 18 H, Me3N)
ppm. 13C NMR (62.9 MHz, [D6]DMSO, 25 °C): δ = 162.1,
146.0, 132.0, 125.4, 121.1, 113.4, 93.4, 88.3, 56.4 ppm.
C84H90I4N6O6Ti·4H2O (1901.19): calcd. C 53.07, H 4.87, N 4.42;
Bis(triethylammonium) Tris{4,5-bis[2-(4-nitrophenyl)ethynyl]-1,2-
benzenediolato}silicate(IV) (10): To a mixture of 1,2-dihydroxy-4,5-
bis[2-(4-nitrophenyl)ethynyl]benzene (8; 100 mg, 249 µmol) and
Et3N (16.2 mg, 124 µmol) in dry MeCN (10 mL) a 1  solution of
Si(MeO)4 (12.1 mg, 77.4 µmol) in dry MeCN was added. The solu-
tion turned orange and was stirred at room temperature for 24 h.
Overnight a solid precipitated which was filtered off, washed with
MeCN and dried in vacuo. Yield 78% (76.0 mg) of an orange solid.
1H NMR (250 MHz, [D6]DMSO, 25 °C): δ = 8.26 (AAЈ, 12 H),
7.73 (BBЈ, 12 H), 6.55 (s, 6 H, 3-H, 6-H), 3.06 (q, 12 H,
CH3CH2N), 1.16 (t, 18 H, CH3CH2N) ppm. 13C NMR (62.9 MHz,
[D6]DMSO, 295 K): δ = 154.6, 146.0, 131.7, 130.5, 124.1, 112.8,
111.9, 97.1, 88.9, 45.8, 8.8 ppm. C78H64N8O18Si (1429.5): calcd. C
65.54, H 4.51, N 7.84; found C 64.13, H 4.38, N 7.56. IR (KBr): ν
˜
= 3071 (w, C–H-aryl), 2197 (m, CϵC), 1591 (s, NO2), 1498 (s),
1384 (w), 1340 (s, NO2), 1244 (s, C–O), 1173 (vw), 1105 (w), 1073
(vw), 891 (w), 852 (w), 795 (w), 748 (w), 711 (vw), 687 (vw), 655
(w), 596 (vw), 565 (vw) cm–1.
found C 53.08, H 4.98, N 4.42. IR (KBr): ν = 3014 (vw, C–H-aryl),
˜
2955 (w, C–H), 2929 (w, C–H), 2885 (w, C–H), 2857 (w, N–Me),
2198 (w, CϵC), 1508 (w), 1479 (s), 1413 (w), 1369 (m), 1278 (w),
1244 (s, C–O), 1200 (w), 1113 (w), 1011 (vw), 955 (vw), 936 (w),
884 (w), 844 (m), 798 (w), 635 (m), 565 (m), 502 (m) cm–1.
1,2-Bis(tert-butyldimethylsilyloxy)-4,5-bis{2-[4-(dimethylamino)-
phenyl]ethynyl}benzene (12): To a mixture of 4,5-bis(tert-butyldime-
thylsilyloxy)-1,2-diiodobenzene (5; 189 mg, 320 µmol), (PPh3)2-
PdCl2 (24.0 mg, 34.2 µmol) and CuII (4.00 mg, 21.0 µmol) in dry
Et2NH (5 mL) (4-ethynylphenyl)dimethylamine (11; 100 mg,
680 µmol) was added. The red solution was heated to 50 °C for
24 h, cooled to room temperature and the solvent was evaporated
in vacuo. The remaining brown solid was purified by chromatog-
raphy on Al2O3 (neutral, act. V; dichloromethane/petroleum ether,
1:9) to yield a colourless solid. Yield 78% (156 mg) of a colourless
Acknowledgments
We thank the Deutsche Forschungsgemeinschaft for financial sup-
port. We also thank Heraeus GmbH and Wacker AG for support
with chemicals and Prof. Dr. J. Heck and Dr. C. Wittenburg (Insti-
tut für Anorganische Chemie, Universität Hamburg) for prelimi-
1
solid. H NMR (250 MHz, [D6]acetone, 25 °C): δ = 7.38 (AAЈ, 4
H), 6.99 (s, 2 H, 3-H, 6-H), 6.72 (BBЈ, 4 H), 2.99 (s, 12 H, Me2N), nary hyper-Rayleigh scattering measurements.
1.02 [s, 18 H, (CH3)3CSi], 0.28 [s, 12 H, (CH3)2Si] ppm. 13C NMR
(62.9 MHz, [D6]acetone, 25 °C): δ = 151.6, 148.0, 133.6, 124.7,
121.2, 113.1, 111.2, 94.5, 87.3, 40.5, 26.6, 19.4, –3.50 ppm.
C38H52N2O2Si2 (625.02): calcd. C 73.03, H 8.39, N 4.48; found C
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Tris(catecholato)metal(,) Complexes with Acceptor-Substituted Ligands
FULL PAPER
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Eur. J. Inorg. Chem. 2005, 4509–4515
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